The present invention concerns a process for the production of 3-methyl-pyridine (3-picoline) from formaldehyde, paraldehyde, ammonia, and acetic acid.
3-picoline is a colourless, flammable liquid which is used as a solvent, for the production of medicaments and insecticides as well as for the synthesis of nicotinic acid and nicotine amide.
Several synthetic routes for the production of 3-picoline are known in the art, which are generally based on an addition/cyclization reaction of aldehyde/ketone mixtures with an ammonia compound. Said reactions can run in the gas phase or in the liquid phase as well as using a catalyst.
The process according to the present invention is based on the publication of Grayson, J. and Dinkel, R., “An improved Liquid-Phase Synthesis of Simply Alkylpyridines”, Helvetica Chimica Acta, Vol. 67 (1984), p. 2100-2110.
The authors of this publication describe in table 2, p. 2108 inter alia the synthesis of 3-picoline from acetaldehyde and formaldehyde, whereby different ammonia sources are compared with regard to 3-picoline yield as well as to the presence of diverse, unwanted side products.
In particular, it is shown that the use of ammonia acetate results in a yield of 44%, whereby 3 ethylpyridine as the main side product is present in an amount of 18%.
Thus. the technical problem to be solved is to improve the process of Grayson and Dinkel with regard to 3-picoline yield, reduction of 3-ethylpyridine amount as main side product as well as an increase in the space/time yield.